1. Field of the Invention
The present invention relates to a method for coating a substrate with an amorphous type titanium peroxide. More specifically, it relates to a method for coating a substrate having a water repellent surface with viscous amorphous type titanium peroxide having excellent adhesive properties, and it also relates to a board having a thin layer of a photocatalytic semiconductor or a dielectric-conductive ceramic material in which the titanium peroxide is used as a binder.
2. Description of the Related Art
Heretofore, as methods for coating a substrate with a photocatalytic semiconductor and a dielectric-conductive ceramic material, there are techniques such as a sputtering method, a vapor deposition method and a high temperature sintering method using a transcription printing film.
As fixing methods of the photocatalytic semiconductor, there are known a method which comprises adding various kinds of organic binders and silica gels and then carrying out heat work (Japanese Patent Application Laid-open No. 171408/1995), a method which comprises using a glaze, an inorganic glass, a thermoplastic resin, a solder or the like as a binder (Japanese Patent Application Laid-open No. 232080/1995), and a method which comprises fixing the photocatalytic semiconductor on a board by the utilization of SnO2 as a coagulation agent (Japanese Patent Application Laid-open No. 155598/1995).
However, the sputtering method and the vapor deposition method require a high cost for a coating apparatus, and in the transcription printing method, a thermal stress which loads on the board or the like must be considered and the selection of a material is restricted.
Furthermore, in a method for fixing the photocatalytic semiconductor and the dielectric-conductive ceramic material by the use of the binder, the surface of the substrate is required to be pre-treated with a surface active agent and a caustic soda solution, when the surface of the substrate is water repellent. Furthermore, it is difficult to sufficiently carry out an oxidation-reduction function and a dielectric-conductive function, because particles of the photocatalytic semiconductor and the dielectric-conductive ceramic material are buried in the binder.
Additionally, as titanium peroxide, in Japanese Patent Application Laid-open No. 286114/1995, there is mentioned a coating solution for film formation comprising peroxopolytitanic acid which is a polymer of peroxotitanic acid. It has also been disclosed therein that this peroxopolytitanic acid can be obtained by adding hydrogen peroxide to a gel or a sol of titanium oxide hydrate or a mixed dispersion thereof, and then treating it at room temperature or heating it at 90xc2x0 C. or less (heating at 80xc2x0 C. for 1 hour in Example 1).
In addition, there is also known a viscous or a jelly state product which can be obtained by condensing an aqueous titanium peroxyhydrate solution (Japanese Patent Application Laid-open No. 252319/1987). It is described therein that this product can be obtained as a yellow film by adding aqueous hydrogen peroxide to a fine powder of titanium hydride to prepare a yellow aqueous titanium peroxide solution, and then allowing it to stand at ordinary temperature, thereby slowly advancing the evaporation of water and the condensation of a solute.
However, peroxopolytitanic acid described in Japanese Patent Application Laid-open No. 286114/1995 mentioned above can be obtained by adding hydrogen peroxide to a gel or a sol of titanium oxide hydrate or a mixed dispersion thereof, and then treating at ordinary temperature or heating it at 90xc2x0 C. or less, and therefore, this peroxopolytitanic acid is different in a preparation process from xe2x80x9cthe viscous amorphous type titanium peroxidexe2x80x9d of the present invention which can be obtained by adding hydrogen peroxide to titanium oxide hydrate, and then carrying out the reaction at 15xc2x0 C. or less. In addition, they are largely different from each other in physical properties, particularly viscosity, and the conventional product is poor in the function as a binder, so that it is difficult to form a thin layer of the photocatalytic semiconductor and the dielectric-conductive ceramic material.
Furthermore, a viscous or a jelly state product which is obtained by condensing an aqueous titanium peroxyhydrate solution described in the above-mentioned Japanese Patent Application Laid-open No. 252319/1987 can be obtained as a yellow film by adding aqueous hydrogen peroxide to a fine powder of titanium hydride to prepare a yellow aqueous titanium peroxide solution, and then evaporating water from this yellow aqueous titanium peroxide solution. Therefore, this conventional product is different in a preparation process from xe2x80x9cthe viscous amorphous type titanium peroxidexe2x80x9d of the present invention which can be obtained by adding hydrogen peroxide to titanium oxide hydrate, and then carrying out the reaction at 15xc2x0 C. or less. In addition, they are different from each other in physical properties. As described in the above-mentioned Japanese Patent Application Laid-open 286114/1995 (the second column), the conventional product has a problem that it is stable only in an extremely low concentration and it cannot be present in a stable state for a long time. Moreover, a thin layer formed from the conventional product on a substrate is easily cracked or peeled off, and the thin layer becomes porous after a high-temperature calcination.
An object of the present invention is to provide a coating material unlimited by thermoplasticity of a substrate which does not need a hydrophilic treatment by the use of a surface active agent and the like, even when the surface of the substrate is water repellent or the substrate is thermoplastic.
Another object of the present invention is to provide a method for forming a film, in which a thin layer of a photocatalytic semiconductor or a dielectric-electrical ceramic material may be easily formed and thickness of the thin layer may be controlled easily and the photocatalytic semiconductor or the like is not buried by a binder.
The present inventors have intensively investigated trying to achieve the above-mentioned objects, and as a result, the present invention has now been completed by fixing the use of a viscous amorphous type titanium peroxide or the like as a binder layer on a substrate, or by attaching fine particles of a photocatalytic semiconductor, a dielectric ceramic material or a conductive ceramic material on a viscous amorphous type titanium peroxide layer in a uniform scattering state of the fine particles in a gas, or by fixing a viscous amorphous type titanium peroxide on a substrate and then heating and calcining it to form a titanium oxide layer having a photocatalytic activity.
That is to say, the present invention is directed to a method for fixing an amorphous type titanium peroxide layer on a substrate which comprises the steps of coating the substrate with an amorphous type titanium peroxide sol, or coating the substrate with a viscous amorphous type titanium peroxide without hydrophilization treatment of a surface of the substrate with a surface active agent or the like, and drying and calcining it at room temperature to less than 250xc2x0 C.; and a board having the amorphous type titanium peroxide layer obtained by this method.
Moreover, the present invention is directed to a method for fixing a titanium oxide layer on a substrate which comprises the steps of coating the substrate with an amorphous type titanium peroxide sol, or coating the substrate with a viscous amorphous type titanium peroxide without hydrophilization treatment of a surface of the substrate with a surface active agent or the like, and drying and calcining it at 250xc2x0 C. or more; and a board having the titanium oxide layer obtained by this method.
Additionally, the present invention is directed to a method for fixing a thin layer of a photocatalytic semiconductor, a dielectric ceramic material or a conductive ceramic material on a substrate which comprises the steps of coating the substrate with an amorphous type titanium peroxide sol, or coating the substrate with a viscous amorphous type titanium peroxide without hydrophilization treatment of a surface of the substrate with a surface active agent or the like, thereby forming an amorphous type titanium peroxide layer, and then attaching fine particles of the photocatalytic semiconductor, the dielectric ceramic material or the conductive ceramic material in a uniformly scattered state in a gas onto the amorphous type titanium peroxide layer, while the amorphous type titanium peroxide layer is still sticky; and a board which comprises a substrate, the amorphous type titanium peroxide layer formed on the substrate, and a thin layer of the photocatalytic semiconductor, the dielectric ceramic material or the conductive ceramic material formed on the amorphous type titanium peroxide layer and which can be obtained by the above-mentioned method.
Furthermore, the present invention is directed to a method for preparing a viscous amorphous type titanium peroxide which comprises the steps of reacting a titanium tetrachloride solution with an ammonium hydroxide solution in an acidic range of pH 2 to 6, washing a sedimented lightly bluish white orthotitanic acid, diluting or concentrating the solution to adjust a solid concentration to 0.2 to 0.6% by weight, adding aqueous hydrogen peroxide to the aqueous solution, carrying out a reaction with stirring at a low temperature, preferably at 15xc2x0 C. or less, particularly preferably at about 5 to 8xc2x0 C., and then curing it at ordinary temperature; and the viscous amorphous type titanium peroxide prepared by this method.